Process for the electrolytic production of metal screens



Dec. 24, 1940. w. BEEBE 2,225,733

PROCESS FOR THE ELECTROLYTIC PRODUCTION OF METAL SCREENS Filed Dec. 10,1937 fig"- 1 INVENTOR W'afimn .Beefie 4 ATTORN-EY Patented Dec. 24, 1940UNITED STATES PATENT OFFICE PROCESS FOR THE ELECTROLYTIC PRO- DUCTION FMETAL SCREENS Applicationnecember 10, 1937, Serial No. 179,108

2 Claims.

This invention, relates to electro-deposition and more particularly tothe formation of screens or other apertured members by electrolyticdeposition of metal to form the desired member.

5 The invention is adaptedfor :use in forminga wide variety of articlesand is especially well adapted for forming fine, accurate screens ormembers having screen portions suitable for such various uses asphoto-engraving screens, artists retouching screens, classifyingscreens, filter screens, protective screens and others.

In accordance with one embodiment of the in; vention, a member, such asa plate, is provided with non-conductive areas forming a patterncorresponding to the apertures ofthe member which is to be formed, andmetal is deposited on the conductive areas of the plate to form thescreen, whereafter the electro-deposited screen is removed from theplate.

The pattern of non-conductive areas may be The printing plate isemployed in printing the desired pattern in non-conductive material ontoF a plate which is to.form a cathode on which the metal screen isdeposited. The design is treated to render it adherent to the cathodeplate. The cathode plate is arranged as a cathode in an electric celland the metal is electrolytically deposited on the conductive areasthereof. The plate with the adherent non-conductive material anddeposited screen may be treated torender the non-conductivematerialadherent t6the plate whereafter the deposited screen is stripped fromthe plate.

,A feature of the'invention is the forming of fine, accurate screen ormembers having screen portions of integral construction and havingapertures of predetermined size and arrangement and which retain sucharrangement during use.

Another feature of the invention is the forming of screen or likemembers having predetermined metallic structure which is uniformthroughout all portions of the structure or which varies in apredetermined manner.

, Still another feature of the invention is the deposition of metaldirectly upon the cathode of an electrolytic cell and the subsequentstripping of the deposited member without the adherence of foreignmatter of any kind. 5 The invention further consists in the new andnovel features of operation and the new and original arrangements andcombinations of steps in the process hereinafter described and moreparticularly set forth in the claims. 10

The invention also consists in forming a product having the generalcharacteristics, the new and useful applications, and the severaloriginal features of utility hereinafter set forth and claimed. 15

It will be understood that the present invention is capable of wideapplication, but for the purposes of illustration, it is. described inconnection with the formation of the screen suitable for use as anartists retouching screen.

For the purpose of illustrating the novel process it is describedhereinafter in connection with one form of apparatus suitable forcarrying out the several steps and operations and illustrated in theaccompanying drawing, wherein Fig. 1 is an enlarged, fragmentary,cross-sec tional view, indicating diagrammatically the initial step inthe process; and

Figs. 2, 3 and 4 are similar views indicating respectively subsequentsteps in the process. 30

A plate I (Fig. 1) (hereinafter called a master plate) is formed frommaterial of sufficient rigidity and surface hardness which can beconveniently etched either electrically or chemically. This plate can beformed from a single material or from a material having a suitable metalcoating. Preferably, the plate is formed from copper, but other metalsmay be used, such for ex ample, as zinc, the so-called J'em metal (whichconsists principally of zinc) or others. The ma- 40 terial should be onewhich is not affected by temperatures employed in vulcanizing rubber.

The master plate is provided with a light sensitive coating 2 (Fig. l)capable of being hardened on exposure to light. Such coating may i beformed from chromated fish glue, as will be understood by those skilledin the art. The light sensitive coating is exposed through one or morephoto-engraving screen plates 3 (Fig. 1), or an enlargement or reductionthereof, in order to form in said coating a light-hardened patterncorresponding to the apertures to be provided in the screen. The coatingis then developed, as by washing in water, to remove the unexposed,unhardenedportions of the coating material.

The pattern may comprise minute areas of socalled dots having variousshapes, such as square, rectangular, circular, elongated and many othersand various combinations thereof. Preferably, it is desirable to providea non-conductive border adjacent the edges of the cathode plate wherebyto facilitate stripping of the screen from the cathode. A suitable areamay be provided for electrical connection of the plate; preferably, thearea is adjacent the edge to permit a clip connection to be engagedthereover- The master plate is then suitably etched to form therein arelief or intaglio design having raised portions 4 (Fig. 2)corresponding to the aperture pattern which is to be produced in thescreen. Although the plate may be etched by a known chemical method, Iprefer to carryout the etching electrolytically by connecting the masterplate as an anode in an electrolytic cell and thereby removing theportions of the plate which are not protected by the insulating coating.The plate preferably is etched to a depth of from 0.006 inch to 0.008inch.

The master plate is removed from the cell and the light-hardenedmaterial may be removed therefrom as by washing in a sodium cyanidesolution or by mechanical abrasion. However, in certain cases it is notnecessary to remove the light-hardened material before proceeding to thenext stop.

The master plate is employed as a mold to produce a matrix 5 (Fig. 2)from suitable moldable material which will accurately reproduce in theform of a negative the relief pattern of the etched master plate.Preferably the matrix is formed from balata by the application ofsuitable heat and pressure, as will be understood by those skilled inthe art. The matrix is employed in molding a printing plate 6 (Fig. 3)from suitable flexible material, such as soft rubber by the applicationof suitable heat and pressure.

The rubber printing plate preferably is secured on a roll of a cylinderprinting press (not shown) and inked with a suitable acid-proof,non-conducting liquid material capable of being hardened and treated tocause it to firmly adhere to a plate I (Fig. 3) which is to form-acathode, as hereinafter described. The cathode plate is run through thepress and a design 8 (Fig. 4) printed thereon which corresponds to thedesign originally formed in the master plate. If desired, the printingplate may be used in an offset printing press, as will be understood, toprint the cathode plate.

The rubber printing plate may be used repeatedly to print the patternonadditional cathode plates. If desired, the same cathode plate can becleaned and reprinted after one or more screens have been formed thereonas hereinafter described.

The cathode plate I is formed from a rustproof, non-corrodible materialof suflioient rigidity and surface hardness and has at least its facesformed of a conductive material, such as a suitable metal or alloy whichpermits the electrolytic deposition of metal directly thereon and thesubsequent stripping of the deposited member without the necessity forusing a parting agent. The face or faces which are to recmve thedeposited metal are made suificiently smooth and level to permitaccurate printing of the design thereon and preferably are provided witha satin finish in order to insure adherence of the deposited metal. Itwill be understood that the elementary metal.

term"cathode plate is intended to mean any suitable form or shape and isnot limited to a member of plate form.

The cathode plate is provided with a non-conducting border (not shown)adjacent the edges, which may be printed simultaneously with the designor pattern. This prevents deposition of the metal adjacent the edges ofthe plate and thus facilitates stripping of the deposited screen; asuitable conductive area may be provided adjacent a portion of one edgeto permit connection of the plate in an electrical circuit.

The cathode plate I with the printed pattern 8 (Fig. 4) is treated inorder to render the nonconducting material adherent. Preferably, this isaccomplished by baking the plate and nonconducting material at atemperature of from 300 F. to 400 F., andpreferably around 350 F., inorder to harden the non-conductive material and cause it to adherefirmlyto the cathode plate.

Where the deposition is to be made on one side only of the cathodeplate, the latter is now ready for insertion in the electrolytic cell.However, it is often desirable to form a similar deposit on both facesof the plate or in certain' cases, dissimilar deposits. Where a depositis to be made on both faces of the plate, the other face' of the plateis provided with a non-conducting pattern as above described.

The cathode plate and a'suitable anode or anodes (not shown) aresupported in an electrolyte corresponding to the material to bedeposited. The anode and cathode plate are connected in a suitableelectric circuit and current is passed through the cell thus formed.

The screen may be formed from a material, such as copper, nickel,chromium, lead, tin, or other non-ferrous metals or alloys orcombinations thereof depending upon the characteristics desired. It willbe understood that, where the term metal is used herein, it is to betaken as meaning metal, one or more metals, alloys, or

one or more alloys and is not limited'to a single,

I have found that screens suitable for a large number of uses may beformed from copper which may, if desired, be provided with a platedcoating or another metal.

Where a copper screen is to be formed, a copper anode is provided andthe electrolyte consists of copper sulphate, sulphuric acid and water insuitable proportions.

The circuit is energized and copper is electrolytically deposited on theexposed, conducting areas of the cathode plates. I prefer to employ acathode plate of suitable composition and characteristics and todispense with the use of a separating or parting agent, such as isusually employed. Thus the deposition can be effected directly onto thebare surfaces of the cathode plate.

Deposition is continued until the desired thickness of material is builtup on the cathode plate to form a screen 9 (Fig. 4) correspondingexactly to the exposed areas of the cathode and having an aperturepattern corresponding to the nonconductive pattern on the cathode plate.Where the screen to be formed is to have a thickness exceeding about0.004 or 0.005 inch, it is preferable to halt the deposition at athickness of about 0.004 or 0.005 inch in order to prevent the aperturescapping over by reason of the deposition of material which fills up theapertures. Further deposition may be carried out after stripping fromthe cathode plate, as hereinafter explained.

The various operating factors such as current density, ratio of anode tocathode area, spacing between the anode and cathode, composition of theelectrolyte, temperatureof the electrolyte, and agitation of theelectrolyte are carefully controlled to provide a deposit of materialhaving the desired hardness, density, grain structure, tensile strength,brightness and the like.

Where it is desired to produce a screen having uniform metallicstructure, the several operating characteristics should be kept uniformthroughout the entire period of deposition. I have also found that it isimportant that the cathode plate be brought to and remain at thetemperature of electrolyte before connecting in the electrical circuit.Thus, it is possible to avoid non-uniformity in metal structure, whichwould otherwise occur owing to the formation of bubbles and othercauses.

When the desired thickness of metal is deposited, the cathode plate isdisconnected from the circuit, removed from the electrolyte, and washedin water. Thereafter, the plate, with the pattern of non-connectingmaterial and the deposited metal, is baked at a temperature of from 300F. to 400 F., and preferably around 350 F. for a suitable period, forexample, approximately three minutes. Thus, whenthe deposited screen isstripped from the cathode plate, the non-conducting material adheres tothe plate with great tenacity and is not removed with the depositedmember.

The deposited member is then stripped from the cathode plate by anysuitable means, as for example, either manually or by suitablemechanical or semi-mechanical means.

'Where it is desired to form a screen exceeding 0.004 or 0.005 inch inthickness, the screen after removal from the cathode may be returned tothe bath and metal deposited on both sides of the screen to build suchscreen to the desired thickness. Thus, a screen can be formed withapertures of substantially uniform diameter throughout the thickness ofthe screen and having side walls extending substantially perpendicularto the faces of the screen.

Preferably, the screen is secured in a suitable frame, as for example, aframe formed from wood 'or synthetic resin or other suitable material,the screen being drawn taut in the frame to prevent uneven deposition ofmetal thereon.

The screen is immersed in the electrolyte, connected as a cathode in theelectric circuit and the. further deposition made of either the same ora different metal.

It, will be understood that screens may be formed by the present processranging in thickness from 0.00025 inch up to any desirable and practicalthickness. Generally, screens for photcgraphic purposes will range inthickness from 0.0015 to 0.002 inch; filter and classifying screens.

' coating of another material, as for example, .nickel, chromium or thelike, which can be done by supporting the screen in a suitableelectrolyte and subjecting it to an electroplating operation. Thepresent invention provides a method of forming an integral, aperturedmember, such as a screen, wherein the apertures are accurately formedand provided with sharp, clean-cut rims. Each face of the screen,including the rims or edges of the apertures, lies in a single plane andthe screen may be made so thin that both faces in effect lie in a singleplane. The side walls of the apertures may be made substantiallyperpendicular to the faces of the screen.

The screen may be formed from any one of a number of metals or alloyshaving characteristics suitable for various uses. The screen may have auniform metal structure, or if desired, the operating conditions may besuitably controlled so that various areas of layers of the metal mayhave different characteristics. For example, the screen may have anydesired degree of flexibility or hardness, and may be made harder in onearea and softer in others.

The invention permits the production of a screen having apertures ofwhich the size and spacing may be absolutely uniform or may vary inaccordance with a predetermined design, but which, in any event, remainthe same during the use and do not vary under the conditions of theintended use.

Since the electro-deposited metal may be deposited in an extremely thincoating and thus the contours of the plate and non-conductive patterncan be faithfully reproduced, and since an accurate pattern can beproduced by printing on the plate, it is possible to produce very'finescreen. Both the apertures and the spacing between the apertures may bemade extremely small. For example, it is possible to produce a screenhaving up to 100 apertures per lineal inch.

Since the printing plate, when once formed, can be employed to print thedesign on a large number of cathode plates or repeatedly on the sameplate, the process can'be carried out very economically. Also, all ofthe screens produced from a single printing plate will be uniform.

By theme of a cathode plate of suitable com position and characteristicsit is possible to deposit metal directly on the plate without the use ofa separating or parting agent, such as has heretofore been considerednecessary. The screen is thus deposited evenly and has a surfacecorresponding to the conductive surface of the cathode plate and whenstripped is bright and clean. The deposited member can be stripped orpeeled from the cathode plate readily and without the use of great forceor the danger of injury to the deposited member or the surface of theplate.

While certain novel features of the invention have been disclosed andare pointed out in the annexed claims, it will be understood thatvarious omissions, substitutions and changes may be made by thoseskilled in theart without departing from the spirit of the invention.

What is claimed is:

1. The method of forming fine mesh metal screens which comprisesdepositing a lighthardenable coating on a metal plate, exposing saidcoating to light through a screen to form a predetermined pattern oflight-hardened material, washing the coating to remove the unexposedportions of light-hardenable material, electrolytically etching theuncoated areas of said member to form a relief pattern corresponding tosaid first pattern, molding a balata matrix constituting a negative ofsaid member, molding from said matrix a.rubber printing plate having apattern corresponding to said first pattern, employing said member toform a reliei pattern corresponding to said first pattern, molding amatrix constituting a negative of said member, molding from said matrixa rubber printing plate constituting a positive and having a patterncorresponding to said first pattern, employing said plate to print saidlast pattern in nonconducting material on a plate, electrolyticallydepositing metal on the unprinted conductive areas of said plate to forma screen and stripping said screen from said plate.' 10

WATSON BEE'BE.

